1. Field of the Invention
The present invention relates to a process and apparatus for electrolytic treatment of a surface and, more particularly, to a process and apparatus which minimizes both treatment time and contamination of the electrolytes.
2. Description of the Related Art
Systems for electrolytic treatment of a surface, especially of a metal strip, are well known. Such systems include at least one container holding an electrolyte through which the strip runs horizontally. Anodic connected and cathodic connected electrodes are arranged above and below a path defining a direction of movement of the strip through the device in alternating fashion one behind the other. These systems are especially useful in pickling, cleaning and degreasing the strip.
A known device of this type is described in European Patent Application No. 02 35 595 and is used for cleaning the surfaces of metal strips. This device is employed in combination with mechanical components that act on the strip surface.
Usually, the entire electrolytic process is carried out in at least one container which contains the electrolyte needed to perform the process. The electrolyte is customarily supplied to the container by pumps.
The electrodes arranged above and below the strip are generally designated as the working electrodes to which the strip acts as a counter-electrode; the method of operation of a device using such an arrangement is referred to as the middle conductor process. As is known, when the electrodes on both sides of the strip have the same polarity all points on the strip surface, regardless of which strip side they lie on, also have the same polarity --i.e. if all of the working electrodes are positive-connected (anodic) then the strip surface acts as a negative pole (cathode) and vice versa.
In prior art processes and devices the current flows not only directly to the strip but also from one working electrode to the next through the electrolyte, thereby forming a short circuit or bridge between adjacent electrodes. Thus, these processes and devices suffer from the loss of a considerable portion of the available electrolytic current due to the short circuit and, in addition, this current is not effective for treatment of the surface as is known from Kirchhoff's Law. Another disadvantage of prior art devices is that when several electrodes are arranged next to one another in alternating order (i.e. anode/cathode/anode...), the electrolyte becomes evenly contaminated with the product being removed from the strip. Furthermore, currently-known devices are also unable to provide an electrolytic cascade.
FIG. 2 shows a prior art device for electrolytic treatment of a surface including a container 1 through which the strip 2 to be treated extends in a substantially horizontal orientation. At the entrance and exit of the container 1 are deflector and guide rollers 3, 4 which supportingly define the position of strip 2 in container 1. Anodic connected 5 and cathodic connected 6 working electrodes are arranged above and below the strip 2 in alternating order along the longitudinal direction of the strip 2.
Short-circuit currents 7 may travel between adjacent cathode connected and anode connected electrodes with the electrolyte acting as a bridge therebetween. These short-circuit currents limit the efficiency of the treatment process as the currents should flow between the working electrodes 5, 6 and the strip 2 to the greatest extent possible for full effectiveness as discussed hereinabove.
It would therefore be desirable to provide a process and apparatus for electrolytically treating a surface which eliminates the formation of short circuit currents between adjacent opposite-polarity electrodes. It would be further advantageous to minimize contamination of the electrolyte by the product being removed from the strip.